API Calls to F5 limited to 1024 KB download

I have reproduced the symptom: 200 OK is received even the file data is partially transferred.

The following curl call against the file 'large.xml' (12,000,000 bytes) responded with 1 MB (1024 * 1024 bytes) only.

curl -D x -sku admin:<pass> https://<host>/mgmt/tm/asm/file-transfer/downloads/large.xml | wc
      0       1 1048576
 
HTTP/1.1 200 OK
...
Content-Length: 1048576

The behaviour is different from the other downloading endpoint. For example,

curl -D x -sku admin:<pass> https://<host>/mgmt/cm/autodeploy/software-image-downloads/BIGIP-12.1.2.0.0.249.iso -H "Content-Type: application/octet-stream" | wc
   3687   13306 1048576 
 
HTTP/1.1 206 Partial Content
Content-Length: 1048576
Content-Type: application/octet-stream
Content-Range: 0-1048575/2011930624

As you can see, the call returns the first 1 MB along with the 206 Partial Content. You can see the size and the location of the partial content from the Content-Length and Content-Range headers.

The location of the above file transfer (download) is /shared/images. If you want to utilize the 206 response and Content-xxx headers, you can move the asm xml file to that location (use /mgmt/tm/util/unix-mv). Note that the asm file name contains additional user information: e.g., instead of just asmPolicy.xml, it is admin~asmPolicy.xml, so specify the name accordingly in the calls.

Again, please refer to Demystifying iControl REST Part 5: Transferring Files.